Such batteries are, for example, disclosed in Patent EP 1202372. They preferably take the form of a thin film. In order to use these batteries in environments imparting significant mechanical stresses, for example watch bracelets, textiles, etc., it is necessary to develop very flexible batteries. Batteries available on the market are not sufficiently flexible, so that utilisation thereof in environments imparting significant mechanical stresses quickly leads to breakage of one of the battery elements. Indeed, cracks appear in the encapsulation material, for example, after being bent several times, leading to deterioration of the battery. Batteries have also been developed in which the current collectors, generally found at the ends of the battery, are used for encapsulation. It is consequently the element that undergoes the highest curvature stress, i.e. tensile stress at the highest (external) radius of curvature, and compressive stress at the smallest internal radius of curvature. Consequently, cracks appear in the current collectors after bending around a hundred times at radii of curvature of less than approximately 1.5 cm. These cracks become more marked with increasing bending and form folds which damage the active layers inside the battery. This results in a decrease in capacitance which becomes increasingly marked and eventually destroys the battery.
Further, in addition to flexibility, a battery must also have excellent gas barrier properties. Indeed, the electroactive materials of lithium-ion batteries, for example, are very sensitive to moisture.